1. Field of the Invention
The present invention relates generally to potentiometers and, more particularly, is directed to a multi-rotation type potentiometer in which a rotation angle of its sliding member is limited to a desired angle.
2. Description of the Prior Art
Multi-rotation type potentiometers have been mass-produced so far and most of them are designed to have a specified rotation angle (specified number of revolution). The number of revolutions or turns of the multi-rotation type potentiometer or its sliding member or its spiral resistance wire generally produced is selected as 3, 5, 10, 15 and 20. Among them, the most numerous is the potentiometer that has the number of revolution selected as 10. However, since the multi-rotation type potentiometer is used in various purposes, it is frequently requested that a multi-rotation type potentiometer has a rotation angle of its sliding member or spiral resistance wire such as 4, 8, 12 and the like different from the above mentioned standard rotation angle.
In most cases, such special multi-rotation type potentiometer was usually made by a hand-made work, such as making new parts for the potentiometer, modifying respective parts of the mass-produced potentiometer and remodelling the existing multi-rotation type potentiometer one by one. As compared with the multi-rotation type potentiometer mass-produced, the thus manually constructed multi-rotation type potentiometer becomes extremely expensive and takes a lot of time for its production. In addition, such potentiometer tends to become a make-shift product and is generally unreliable in efficiency and in quality.
It is, on the other hand, proposed that two sliding members are incorporated into a mass-produced standard multi-rotation type potentiometer and rotation angles of the sliding members of the potentiometer are adjusted within a range smaller than a rotation angle of the potentiometer at every rotation of an integer by short-circuiting the two sliding members. However, particularly when this adjusting method is applied to the multi-rotation type potentiometer that is frequently used as a precision potentiometer, there arise the following defects.
That is, the rotation angle of the sliding members and the resistance value of the potentiometer are adjusted by using the two sliding members so that these sliding members increase the contact points to five positions unlike the standard potentiometer having three contact points at most. As a result, the increase of the contact points gives rise to the increase of the mal-contact of the sliding members.
Further, since a contact made of a noble metal is used as the contact portion of the sliding member of the potentiometer, the number of the contact portion which is most expensive in the parts of the potentiometer is increased. Hence, the manufacturing cost of the potentiometer is increased.
Furthermore, there occurs a problem on the linearity which is the most important factor of the multi-rotation type potentiometer. That is, while two separate sliding members are slidably moved on and along the resistance element, they short-circuit the resistance element so that the short-circuit interval of the resistance element is fluctuated dependent on the rotary positions of the sliding members. Thus, different from the inherent linearity of the resistance element, the linearity of the multi-rotation type potentiometer is deteriorated by the fluctuation of the short-circuited interval by the sliding members.
Furthermore, since there are used two sliding members, the number of sliding contacts on the resistance element is increased, thus reducing the life span of the multi-rotation type potentiometer.
Therefore, according to the prior art method as described above, the multi-rotation type potentiometer produced in this way becomes expensive and poor in quality as compared with the standard multi-rotation type potentiometer mass-produced.